Boom apparatus



Dec. 31, 1968 F. D. PETERSON 3,41,046

BOOM APPARATUS Filed Sept. 26, 1966 F I G- l 4'" INVENTOR I FREDD. PETERSON B BY ATTORNEYS 3,419,046 BOOM APPARATUS Fred D. Peterson, San Mateo, Calif., assignor to Peterson Products of San Mateo, lnc., Belmont, Calif. Filed Sept. 26, 1966, Ser. No. 581,902 2 Claims. (Cl. 138153) ABSTRACT OF THE DISCLOSURE A multiple-sided tubular reinforced boom including in at least opposite sides thereof prestressed glass fiber strands. In a further embodiment, the strands are concentrated at the multiplicity of corners of the boom to provide added tensile and compressive strength.

The present invention relates in general to a boom structure and its method of preparation. More particularly, this invention is directed to a structurally reinforced boom prepared from materials having a high dielectric coefiicient.

The principal technique employed for manufacturing dielectric boom structures has heretofore been through the helical winding of synthetic fibers on a precision machined steel mandrel and thereafter impregnating the fibrous structure with an adhesive resin in order to form an integral unit. This method is costly in that the steel mandrel must be precision machined to avoid any slight imperfections in the structure or surface of the mandrel which would prevent extraction of the mandrel from the completed boom. Even when such precautions are taken, extraction of the completed boom from the machined mandrel is still difficult at best.

Another undesirable aspect of this conventional method of construction lies in the resulting spiral orientation of the fibers making up the boom. The fibers are generally helically arranged, and, therefore, provide little longitudinal compression and tension strength when the boom is employed as intended. Furthermore, the conventional methods of preparation are primarily adapted for circular booms. This is obviously disadvantageous when a boom having some other cross section is desired since fibers which are positioned under tension during winding will tend to change from whatever cross section or configuration is initially formed to a generally circular cross-sectional configuration when the mandrel is removed.

Broadly stated, the present invention, to be described in greater detail below, is directed to a boom structure and method for making the same wherein the boom is formed on a multi-sided mandrel wherein synthetic glass fiber strands, such as conventional Fiberglas, are disposed longitudinally in similar amounts under slight tension generally along opposite sides of the mandrel. Various interleaving materials, of lower tensile strength, are provided both over and under the longitudinal strands and along the remaining sides of the mandrel to concentrate the strength of the boom on opposite sides at the longitudinal fiber strands in the manner of an I-beam. The interleaving side portions provide sufiicient structural rigidity to hold the longitudinal reinforced sides at the desired spaced-apart location. More particularly, the underlayer is first formed over a shim which is disposed around a substantial portion of the mandrel. Before the longitudinal strands are applied over the underlayer, this shim is removed. This insures that any shrinkage which may occur will not prevent the final boom structure from still being easily extracted from the mandrel.

It is a principal object of this invention to prepare a boom structure, having a high dielectric strength, as well as high compression and tension strength.

It is a further object of this invention to prepare a States atent boom in such a manner that it will be easily and quickly removed from the mandrel upon which it is formed.

It is a feature and advantage of this invention to employ materials which are translucent so that imperfections formed in the layers of the synthetic materials will be visible during the boom fabrication.

It is a further feature and advantage of this invention to employ a mandrel having a dark outer surface which will aid in the visual observation of imperfections in boom construction.

These objects, features and advantages of the invention will be better understood and others will become apparent when reference is made to the following disclosure, especially in view of the attached drawing wherein:

FIG. 1 is a cut away perspective view of one embodiment of the invention;

FIG. 2 is a cross-sectional view of an intermediate boom structure prior to removal of the shim; and

FIG. 3 is an enlarged fragmentary cross section illustrating the partially formed boom structure after the shim has been removed and replaced with loosely packed matting.

Briefly, in accordance with one aspect of the present invention, a multiple-surfaced mandrel is first prepared having external dimensions which correspond to the internal dimensions desired for the resulting boom. The mandrel is provided with a shim which is disposed to cover adjoining side surfaces and extend around about of the mandrels periphery.

An initial multiple-component resin-type coating of conventional synthetic fibrous materials is applied to the outer surface of the shim and exmsed mandrel to form an underlayer. This underlayer is then slit longitudinally along one side thereof so that the shim may be removed from its position between the mandrel and the coating. The space left by the shim must be of sutficient width to at least allow for the subsequent shrinkage of the synthetic materials which form the boom structure. As a result thereof, the partially finished boom will not adhere tightly to the surface of the mandrel. Therefore, it will be easy to remove the mandrel once the boom is completed.

It is preferable to employ a shim of suflicient thickness so that, for example, additional material can be loosely packed Within the space which remains after the shim is removed. By employing this particular method for the formation of the boom, accurate internal dimensions are obtained while at the same time the necessary compensation is made for the inherent slight shrinkage of the synthetic fibrous layers of which the boom is formed.

After the space left by the shim is filled with loosely packed resin-type material, the longitudinal slit in the underlayer is resealed. Additional fibrous resin support layers are then placed around the initial coating.

Glass fiber-type strands are then strung, under slight tension, along the length of at least two opposed surfaces of the mandrel. 'Phe strands, as well as the previous fibrous layers, are structurally maintained in the desired position by bonding with a conventional adhesive resin. Thereafter, other layers of synthetic fibrous materials are disposed over all the surfaces of the mandrel including those upon which the longitudinal strands have been strung. Finally, the outer surface is finished as desired.

The materials which are specifically set forth throughout this specification are merely representative of the numerous commercially available products which can be employed when practicing the instant invention. It will be obvious to one skilled in this art that many other types of materials will be equally applicable in carrying out the instant invention. Therefore, no attempt has been made to supply an exhaustive list of suitable materials.

By way of example reference is now made to the drawing, wherein similar characters of reference represent corresponding parts in each of the several views, there is shown a boom A prepared as herein set forth.

Referring first to FIG. 2, mandrel B is preferably of a hollow octagonal shape and composed of plywood members 10, 10', 10" and 10', The members 10, 10, 10" and 10" are initially disposed in a rectangular cross-sectional configuration. A triangular section is then removed from each corner. By employing a mandrel of this octangular-type cross section, for example, it has been found that the glass fiber-type strands can be concentrated in the corners of the boom cross section and thereby produce a dielectric structure of extremely high tensile and compression strength.

Mandrel B is first covered with a layer of Formica 11 which is secured along the external sides of members 10, 10, 10" and 10" to insure a smooth surface upon which boom formation can be accomplished. Shim 12, preferably about thick, is disposed around and secured in any conventional manner such as, for example, by taping, to about 180 of the periphery of the Formica covered mandrel B. Shim 12 may be of any suitable smooth surfaced material such as Formica or a similar plastic sheet material. The resulting outer surface is then polished and waxed to further insure a smooth contacting surface to which the synthetic fibrous materials are to be applied.

In order to prevent bonding of the synthetic materials to the outer surface of the polished mandrel, as well as enhance the ease with which the finished boom can be removed from the mandrel, a conventional parting agent such as, for example RAM PVA, can be applied thereto. Furthermore, it has also been found to be advantageous to either utilize dark colored, i.e., black, mandrel materials or darken the outer surfaces of both the Formica 11 and shim 12. This insures that air bubbles or other imperfections which may be present in the subsequent layers of the translucent synthetic materials from which the boom is formed will be easily visible. As a result of early observation, such imperfections can then be corrected during boom fabrication and prior to completion. In this manner, production of a boom structure which is subsequently found to be structurally defective will be prevented.

' Layers of gel such as that available under the trade name Gel-Coat #323 from Diamond Alkali Co., are sprayed over the entire outer surface of mandrel B, preferably in sufficient coats to produce a final dried gel of thickness 13, preferably of about 0.025 inch. Thereafter, discontinuous (chopped) glass fibers in the form of matting 14, are applied over dried gel thickness 13 and bonded thereto with a conventional adhesive resin. The combination of fibrous matting 14 and gel thickness 13 forms an integral undercoating layer on mandrel B.

Chopped glass fiber materials are commercially available in many forms such as Mat #219 from the Owens- Corning Company. Similarly, adhesive resins such as Dion 326, are available from Diamond Alkali Co. In addition, other suitable adhesive resins are discussed in greater detail in the McGraw-Hill Encyclopedia of Science and Technology, 1960, vol 1, pp 67-70u The integral coating layer of gel thickness 13 and matting 14 is then slit longitudinally, for example, along member 10", forming slit 17. The layer is spread aside and shim 12 removed from Formica covered mandrel B. The removal of shim 12 allows for shrinkage to occur without producing a boom structure which is ditficult to remove from the mandrel. Furthermore, accurate internal dimensions can be maintained even during the application of subsequent layers of materials merely by controlling the thickness of shim 12.

It is preferred that the space resulting from the extraction of shim 12 be loosely packed with, for example,

additional chopped glass fiber matting 14'. Strip 1-8, of a suitable fluid-impervious material, is placed between the loosely packed matting 14 and slit 17. This placement of strip 18 insures that any adhesive resin employed to solidify subsequent layers of boom materials will not seep through the boom materials, contact the surface of mandrel B and cause sticking of boom A to mandrel B. Preferably, the intergral coating layer clamped to close slit 17 and additional matting 14 is placed in slit 17 as illustrated in FIG. 3. Matting 14 is bonded in position with additional adhesive resin.

A plurality of layers 15, preferably of commercially available glass fiber-type woven roving mat such as is available from Fiberglas Industries in the form of ROV- Mat 1615, is then placed over matting 14. Each of the mate layers 15, when properly positioned is also treated with adhesive resin to solidify it into the desired position. should metallic inserts (not shown) be desired in the final boom structure, for example, for the attachment of pulleys, lines and the like, it has been found most convenient to place such inserts among layers 15.

Dams (not shown) are preferably attached so as to extend parallel with and outwardly along plywood members 10 and 10". The areas formed between these dams and the sloping outer surface of mat layers 15 are then filled with longitudinally disposed strands 16 of a suitable high strength fiber glass which are strung under slight tension. In this manner the outer octagonal configuration of the intermediate boom structure is built up until the outer cross section is rectangular, Strands 16 are also strung under slight tension over layers 15 along the parallel opposed portions of sides 10' and 10" of mandrel B. Strands 16 can be most easily disposed under tension by weaving them back and forth around a series of pins (not shown) placed at the opposite ends of appropriate surfaces on mandrel B. As a result of this placement of tensioned strands 16, a boom structure having rectangular outer dimensions is produced.

Fiber glass strands 16 are also bonded together and to layers 15 with a conventional adhesive resin as previously described. After the resin has cured, the dams and pins are removed and additional chopped fiber matting 14' is employed to build up the other sides of boom A adjacent plywood members 10 and 10" to a thickness corresponding to the thickness of the sides of boom A along members 10' and 10" (which are covered by strands 16). Additional matting 14" can then be disposed around the entire boom periphery and adhesive resin employed to bond matting 14 in place.

Any shrinkage which occurs in boom A is absorbed by loosely packed matting 14. Therefore, boom A, when completed, is quickly and easily removed from mandrel B and matting 14' is also removed. In finishing the outside surface of boom A, the corners are preferably rounded and the sides smoothed to accurate dimensions by grinding, for example, on a table traverse grinder.

A glossy finish is supplied by adding a coating of adhesive resin. This produces an outer surface which is sufficiently pliable to avoid being dented during use. Furthermore, this resulting smooth surface will avoid dust collections which could produce undesired electrostatic charges along the outer surface of boom A.

By way of particular example, a boom was prepared in the manner set forth above on a hollow plywood mandrel 6" x 8" x 14'. Triangular segments, having dimensions of 2" x l (with the 2" dimension on the 6" sides of the mandrel), were removed from the plywood mandrel.

The resulting 13' rectangular boom had outside dimensions of about 7" x 9" and was found to defiect about 13" under a 17,000 lb. load, yet was not damaged even during repeated applications of similar loadings.

Although one embodiment of the invention has been particularly shown and described, it will be apparent that other adaptations and modifications can be made without departing from the true scope and spirit of the invention.

What is claimed is:

1. A tubular reinforced boom exhibiting a high dielectric coefficient, said boom having an outer configuration including a pair of opposed sides and being adapted for supporting a load that applies compression and tension to said opposed sides, comprising: at least a first layer formed of a mat of short segments of glass fibers, said first layer defining a continuous internal surface of said boom; at least a second layer of glass woven roving integral with said at least first layer; at least a third layer formed of a mat of short segments of glass fiber, said third layer generally defining the external surface of said boom; and a plurality of prestressed glass fiber strands each disposed generally parallel to the longitudinal axis of said boom and between said second and third layers at said pair of opposed sides, wherein the structural strength of said boom will be concentrated along said opposed sides.

2. A tubular reinforced boom in accordance with claim 1 wherein said plurality of strands are concentrated in the corners of said boom as defined by said opposed sides.

References Cited UNITED STATES PATENTS Kempton 138-153 XR Whiting 138-153 XR Noland 156-161 XR Shobert 138-153 XR Martin 156-161 Inghram et a1. 239-165 XR Gorcey et a1 138-153 Dubois.

Shobert 138-174 Clark 138-174 US. Cl. X.R. 

